1. Field of the Invention
The present invention relates to a boot attached to, for example, a steering apparatus of a rack pinion type steering or the like.
2. Related Art
A steering boot covers a ball joint between a steering gear box and a tie rod. That is, one end of the steering boot is fixedly attached to an end of a steering gear box. Further, the other end of the steering boot is fixedly attached to the tie rod. The steering boot is arranged to be proximate to an engine. Therefore, an environmental temperature at a vicinity of the steering boot is a comparatively high temperature. Therefore, air hermetically sealed inside of the steering boot is expanded.
FIG. 4 shows a side view in an axial direction of a steering boot. As shown by the drawing, when air at inside of the steering boot 100 is expanded, the steering boot 100 is expanded to deform. Further, the steering boot 100 meanders to wave in an S-like shape between an end of a steering gear box 102 and an end of a tie rod 103. When the steering boot 100 meanders, the steering boot 100 is brought into sliding contact with a ball joint (not illustrated) or a clamp included therein. Therefore, there is a concern that the steering boot 100 malfunctions. Further, the steering boot 100 is made of a resin. Therefore, once the steering boot 100 meanders to deform, even when the steering boot 100 is cooled, the steering boot 100 is difficult to recover to an original shape.
In this respect, JP-A-10-238629 introduces a steering boot restrained from meandering. According to the steering boot described in the reference, bottoms of three pieces of bellows counted from one thereof fixedly attached to an end of a steering gear box are recessed with peripheral grooves in a U-like shape. Therefore, a rigidity in a diameter direction of the bellows having the peripheral grooves is made to be higher than a rigidity in the diameter direction of bellows of the other portions. Therefore, the steering boot described in the reference is difficult to meander.
However, according to the steering boot described in the reference, in order to increase the rigidity, it is necessary to form the peripheral groove which is not directly related to a function inherent to the bellows. Therefore, according to the steering boot described in the reference, a number of steps of working a die is large and cost is high. Further, by providing the peripheral groove at the bottom portion of the bellows, a rigidity in a direction of elongating and contracting the bellows is reduced and there is a possibility that a portion thereof which meanders to deform is liable to interfere with the clamp fixedly attached to the end of the steering gear box.
In view of the above-described problem, it is an object of the invention to provide a boot in which a number of steps of working a die is small, cost is low and meandering can restrained.
(1) In order to resolve the above-described problem, a boot of the invention is characterized in a boot made of a resin for covering a ball joint interposed between a large diameter mating member and a small diameter mating member, the boot including a large diameter attachment portion fixed to the large diameter mating member, a first bellows portion continuous to the large diameter attachment portion, a second bellows portion which is continuous to the first bellows portion and in which at least a bottom inner diameter thereof is not larger than a bottom inner peripheral diameter of the first bellows portion and a rigidity in a radial direction thereof is lower than a rigidity in a radial direction of the first bellows portion, a taper bellows portion continuous to the second bellows portion, and a small diameter attachment portion continuous to the taper bellows portion and fixed to the small diameter mating member.
That is, the boot of the invention is arranged with the first bellows portion making the rigidity in a radial direction higher than that of the second bellows portion while maintaining an axial direction rigidity thereof to a degree equivalent to that of the second bellows portion. According to the boot of the invention, meandering can be restrained by comparatively simple means of changing the inner peripheral diameter of the bellows portion. Therefore, a number of steps of working a die is small and cost is low. Further, according to the boot of the invention, the first bellows portion is difficult to deform by increasing the rigidity in a radial direction while maintaining the axial direction rigidity and therefore, the first bellows portion is difficult to be brought into sliding contact with a clamp of the larger diameter attachment portion.
(2) Preferably, there may be constructed a constitution in which the bottom inner peripheral diameter of the first bellows portion is not larger than 1.3 times of the bottom inner peripheral diameter of the second bellows portion. More specifically, a multiplication factor of the bottom inner peripheral diameter of the first bellows portion from that of the second bellows portion is equal to or larger than 1.0 and less than 1.3. Here, the bottom inner peripheral diameter of the first bellows portion is set to the bottom inner peripheral diameter of the second bellows portion multiplied by the multiplication factor equal to or larger than 1.0 because when the multiplication factor is less than 1.0, a difference is difficult to be brought about between the rigidities of the first bellows portion and the second bellows portion. That is, because when both of the first bellows portion and the second bellows portion are provided with high rigidities, a function of being elongated and contracted and bent inherent to the bellows is deteriorated. Further, both of the first bellows portion and the second bellows portion are provided with low rigidities, the above-described meandering is liable to be brought about.
On the other hand, the inner peripheral diameter of the first bellows portion is set to the bottom inner peripheral diameter of the second bellows portion multiplied by the multiplication factor equal to or smaller than 1.3 because when the multiplication factor exceeds 1.3, the difference between the diameters is excessively increased and there is a concern that the first bellows portion does not achieve the function of being elongated and contracted and bent inherent to the bellows.
(3) Preferably, there may be constructed a constitution in which at least a pivotal center of the ball joint is contained on an inner peripheral side of the second bellows portion, and the bottom inner peripheral diameter of the second bellows portion is equal to or slightly larger than an outer peripheral diameter of the ball joint.
According to the constitution, the second bellows portion deformed further predominantly than the first bellows portion is brought into contact with the ball joint soon after starting to deform. The second bellows portion is not deformed further by being restricted by the ball joint.
In this way, according to the constitution, the first bellows portion can be restrained from being deformed by the high rigidity of its own and the second bellows portion can be restrained from being deformed by being brought into contact with the ball joint, respectively. Therefore, not only meandering of the first bellows portion but also meandering of the second bellows portion can be restrained.
(4) Preferably, there may be constructed a constitution in which the bottom inner peripheral diameter of the second bellows portion is the outer peripheral diameter of the ball joint multiplied by a multiplication factor equal to or larger than 1.0 and less than 1.25 in the above-described constitution of (3). Here, the bottom inner peripheral diameter of the second bellows portion is set to the outer peripheral diameter of the ball joint multiplied by the multiplication factor equal to or larger than 1.0 because when the multiplication factor is less than 1.0, the boot is difficult to be mounted to the outer peripheral side of the ball joint. Further, because pivotal movement of the ball joint is excessively restrained by interference with the second bellows portion.
On the other hand, the bottom inner peripheral diameter of the second bellows portion is set to the outer peripheral diameter of the ball joint multiplied by the multiplication factor equal to or less than 1.25 because when the multiplication factor exceeds 1.25, an amount of deforming the second bellows portion to be brought into contact with the ball joint is increased. That is, because meandering cannot sufficiently be restrained.
(5) Preferably, there may be constructed a constitution in which an end portion of the ball joint is contained in the taper bellows portion in the above-described constitution of (3). According to the constitution, the taper bellows portion is brought into contact with the end portion of the ball joint soon after starting to deform. The taper bellows portion is not deformed further by being restrained by the ball joint. According to the invention, not only meandering of the first bellows portion and the second bellows portion but also meandering of the taper bellows portion can be restrained.
According to the invention, there can be provided the boot in which a number of steps of working the die is small, the cost is low and meandering can be restrained by arranging the first bellows portion increasing the rigidity in a radial direction continuous to the large diameter attachment portion while maintaining the axial direction rigidity to a degree equivalent to that of the second bellows portion.